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Lanthanide Chemistry: From Coordination in Chemical Complexes Shaping Our Technology to Coordination in Enzymes Shaping Bacterial Metabolism Norma Cecilia Martinez-Gomez,*,† Huong N. Vu,‡ and Elizabeth Skovran‡ †
Department of Microbiology and Molecular Genetics, Michigan State University, 567 Wilson Road, East Lansing, Michigan 48824, United States ‡ Department of Biological Sciences, San José State University, 1 Washington Square, San José, California 95192, United States S Supporting Information *
ABSTRACT: Lanthanide chemistry has only been extensively studied for the last 2 decades, when it was recognized that these elements have unusual chemical characteristics including fluorescent and potent magnetic properties because of their unique 4f electrons.1,2 Chemists are rapidly and efficiently integrating lanthanides into numerous compounds and materials for sophisticated applications. In fact, lanthanides are often referred to as “the seeds of technology” because they are essential for many technological devices including smartphones, computers, solar cells, batteries, wind turbines, lasers, and optical glasses.3−6 However, the effect of lanthanides on biological systems has been understudied. Although displacement of Ca2+ by lanthanides in tissues and enzymes has long been observed,7 only a few recent studies suggest a biological role for lanthanides based on their stimulatory properties toward some plants and bacteria.8,9 Also, it was not until 2011 that the first biochemical evidence for lanthanides as inherent metals in bacterial enzymes was published.10 This forum provides an overview of the classical and current aspects of lanthanide coordination chemistry employed in the development of technology along with the biological role of lanthanides in alcohol oxidation. The construction of lanthanide− organic frameworks will be described. Examples of how the luminescence field is rapidly evolving as more information about lanthanide−metal emissions is obtained will be highlighted, including biological imaging and telecommunications.11 Recent breakthroughs and observations from different exciting areas linked to the coordination chemistry of lanthanides that will be mentioned in this forum include the synthesis of (i) macrocyclic ligands, (ii) antenna molecules, (iii) coordination polymers, particularly nanoparticles, (iv) hybrid materials, and (v) lanthanide fuel cells. Further, the role of lanthanides in bacterial metabolism will be discussed, highlighting the discovery that lanthanides are cofactors in biology, particularly in the enzymatic oxidation of alcohols. Finally, new and developing chemical and biological lanthanide mining and recycling extraction processes will be introduced.
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INTRODUCTION Lanthanides in a Nutshell. While first discovered in 1794, lanthanides were not characterized until 100 years later, primarily because these elements are highly insoluble and scarce in pure form.3,12 Lanthanides consist of 15 elements, from lanthanum (Z = 57) to lutetium (Z = 71), and have high coordination numbers. For decades, it was thought that only specific lanthanides had redox chemistry, limited to Ce4+/Ce3+ and Ln3+/Ln2+ where Ln = La, Sm, Eu, and Yb.13−15 However, redox chemistry has now been demonstrated for all elements in the series.13,14 Lanthanides are also known as 4f elements because their electrons have a partial occupation of the 4f shell. f orbitals are well shielded by the filled 5s, 5p, and 6s subshells.1,2 These electronic configurations result in ligand-field effects for the trivalent ions on the order of 500 cm−1 (6 kJ mol−1), equivalent to a 20−60-fold lower effect than for the d-transition-metal ions.2,16 Further, the stereochemistry of lanthanide complexes is © XXXX American Chemical Society
directed by steric properties of the ligands, whereas the spectroscopic and magnetic properties are not affected greatly by the environment of the metal ion.1,2 Lanthanide contraction results from the large ionic radii of these elements; as the atomic number and charge density increase, the ionic radii decrease.17 This phenomenon is a unique characteristic of lanthanide metals. The ionic radii for the elements in the middle of the lanthanide series are comparable to the ionic radius of Ca2+. Lanthanide contraction not only affects the chemical synthesis of lanthanide complexes, it also affects biological systems. For example, displacement of Ca2+ is observed in tissues, which can affect the bone integrity or block Ca2+ channels and influx into the cytosol.18 Special Issue: New Trends and Applications for Lanthanides Received: April 13, 2016
A
DOI: 10.1021/acs.inorgchem.6b00919 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry The electronic configurations of lanthanides are 5d16s2 for La, 4f m5d16s2 for Ce (m = 1), Gd (m = 7), and Lu (m = 14), 4f n6s2 for Pr−Eu (n = 3−7), and Dy−Yb (n = 9−14).2,24 Divalent lanthanides can have the electronic structure 4f n‑15d1, while trivalent lanthanides have a 4f n configuration, where n has values of 0−14.2,14,16 Lanthanides are strong Lewis acids that coordinate with hard bases (carboxylates)19 and highly electronegative donors such as N or O. Coordination with water is also often found.12 The synthesis of numerous lanthanide complexes relies on the Lewis acid reactivity of these elements,12 as is the case for biological complexes [i.e., protein−pyrroloquinoline quinone (PQQ )−lanthanide interactions]. While lanthanides are relatively abundant in Earth’s crust, they exhibit low aqueous solubility, limiting their biological accessibility.3,12 This led biologists and enzymologists to believe that lanthanides were unlikely to inherently drive enzyme activity in biological systems.10 The finding that lanthanides such as lanthanum (La3+) or cerium (Ce3+) are required for the activity of the PQQ-dependent bacterial methanol dehydrogenase (MeDH), XoxF, has opened a new field of biological study. On the basis of the ability of lanthanides to affect the growth of a variety of organisms,18,20,21 it is possible that lanthanides may affect the catalysis of additional enzymes from diverse metabolic pathways and biological systems.11,20−24
luminescence can be tuned by introducing suitable π-conjugated ligands. The introduction of these ligands allows electronic transfer between lanthanide ions that otherwise would only present weak emissions, an effect known as the antenna effect. Antenna ligands allow Ln3+ complexes to absorb ultraviolet light and enable a weak luminescent metal to give strong visible and near-IR emissions. Because lanthanide trivalent ions have low molar absorptions (less than 10 M−1 cm−1), ligands are employed to transfer energy to the lanthanide, leading to enhanced luminescence.32 Widely used antenna molecules include complexes in which the chromophoric unit is covalently linked to a multidentate ligand (i.e., polyamine, quinoline, and phenanthroline derivatives) that binds to the lanthanide ion.32−34 These complexes are kinetically inert and highly stable, but energy transfer is not efficient.32 Alternatively, the chromophoric unit can be bound directly to the lanthanide ion using carboxylates, aminocarboxylates, or phosphonates, which allows for a more efficient transference of energy onto the luminescent lanthanide trivalent ion.12 Recently, lanthanide β-diketonate and lanthanide β-triketonate compounds have been developed. These complexes are valuable for luminescence applications such as optical signaling, bioimaging, and night-vision devices.35 Lanthanide β-triketonate structures have near-IR emissions, and Yb3+ is the preferred lanthanide for synthesis. A recent successful synthesis reported an assembly of a tetranuclear metallic core using the ligand tribenzoylmethane and a Yb3+ ion in the presence of potassium hydroxide and ethanol (Figure 1).35 The resulting complex produced
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LANTHANIDES IN CHEMISTRY: SYNTHESIS OF LANTHANIDE COMPLEXES Lanthanide complexation in water requires strong coordinating ligands because the hydration enthalpies are large for elements with such high atomic numbers. In nonaqueous conditions, solvation is prevalent. The geometrical arrangement in a lanthanide complex depends on the steric properties of the ligands. Common lanthanide coordination numbers are 8 and 9, promoting coordination polyhedra that can deviate from the idealized symmetrical structures of lowest energy calculated on the basis of n identical lanthanide−ligand bonds. The deviation increment is proportional to the ligand complexity.25 Complexes of metals with large coordination numbers do not need much energy to reorganize one polyhedron to another. Common organic molecules used to construct lanthanide complexes are polydentate ligands (i.e., carboxylates), pyridine ligands, porphyrins, silylamides, aliphatic amides, and Schiff base ligands.26 Complexation with Schiff base ligands has been extensively developed to synthesize macrocyclic complexes. Macrocyclic Structures. Selectivity for coordination chemistry using lanthanides works better when an induced-fit principle or flexible ligands are applied. Macrocyclic structures (up to 14-membered cyclen) contain flexible ligands with pendant coordinating arms that can adjust the coordinating cavity where the metal ion rests.27 The most commonly used macrocyclic structures are known as calixarenes. Separation of different lanthanides from each other using calixarenes is not an efficient process; however, by addition of intramolecular spacers (such as carboxymethylphosphoryl groups) to promote hydrogen bonding, increased selectivity among lanthanides can be achieved.28 In general, these complexes are used for magnetic resonance imaging and optical analytical sensors.29−31 Antenna Molecules for Lanthanide Luminescence. It is interesting to consider differences in emissions from lanthanides among the lanthanide series. Eu3+ and Tb3+ ions produce intense emissions in the visible region,11 while Nd3+ and Yb3+ ions exhibit emissions near the IR region.11 Lanthanide
Figure 1. Structure of a lanthanide β-triketonate complex. Complexation of Yb3+ with a tribenzoylmethane ligand (LH) is depicted. The production of a bimetallic (Yb3+/K+, ratio 2:2) is observed in the assembly. This complex is highly stable and has a high quantum yield. Reproduced with permision from ref 35 Copyright 2014 Royal Society of London.
[Yb(K·HOEt)(L)4]2, where K is potassium, HOEt is ethanol, and L is a ligand. In the complex, the Yb ion is not coordinated directly with the solvent and therefore displays its characteristic emission in the solid state for longer periods of time. Once this antenna molecule was incorporated into an organic light emission device, it proved to be the most efficient near-IR organic light emission device reported to date.35 Coordination Polymers. Coordination polymers are built from metal ions and multidentate inorganic and organic ligands. They are broadly used for nanotechnology and the synthesis of single-molecule magnets (SMMs) that can be used in highdensity data storage technologies, molecular spintronics, and quantum computing devices.36 The design and synthesis of pure lanthanide SMMs are challenging as a result of the flexible coordination sites of lanthanides. However, lanthanide B
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incorporated into promising systems for sustainable energy production such as proton-exchange membrane fuel cells, which are widely used in the automotive industry.39 The oxygen reduction reaction is the most important reaction used for energy conversion in fuel cells and occurs at the cathode. One caveat of using this technology is that the kinetics of the conversion are very slow. The inclusion of platinum (Pt)-based catalysts has been shown to improve the efficiency of the reaction;39 however, Pt-based catalysts are very expensive. An efficient alternative has been to replace pure Pt for alloys of Pt with transition metals such as nickel and cobalt.40 EscuderoEscribano et al. stated that Pt−lanthanide alloys are not only the most “efficient catalysts reported to date for the conversion of the oxygen reduction reaction but are also highly resistant to degradation”.39 Further, by studying the differences between Pt−lanthanides of La3+, Ce3+, Sm3+, Gd3+, Tb3+, Dy3+, or Tm3+, the authors found that the lanthanide contraction effect allows for tuning of the activity and stabilization of these catalysts (Figure 3).
incorporation into the synthesis of these structures is ideal because lanthanides have similar atomic radii throughout the series but very different magnetic and optical properties from each other. These properties allow for a general design of the organic framework.37 Research is focused on the engineering of new functional materials and dimensions to make the synthesis of these molecules easier.38 The assembly of these materials includes the design of a secondary building unit (containing the metal cluster) that is connected by polytopic linkers to extended networks. Functional bridging ligands include cyanides bound to d transition metalates, hydroxides, halogenides, nitrates, polyoxometalates, and carboxylic acids.12 While coordination polymers are instrumental in lanthanide nanotechnology, heteronuclear lanthanide-based coordination polymer synthesis leads to the production of toxic byproducts. To synthesize nonhazardous coordination polymers, microcrystalline powders that are subsequently dispersed as nanoparticles in glycerol have been reported.38 Further, a recent report by Neaime et al. showed that the particle size can be tuned for both luminescence properties and size distribution depending on the solvent used (Figure 2).38
Figure 3. Schematic view of the bulk structure of a lanthanide electrocatalyst. (A) Mixed layer of Pt (gray spheres) and Tb (purple spheres) showing rearrangement after compression and after acid treatment. At least two layers of Tb will be leached, compressing the structure. (B) Kinetic current density (jK) of the alloys at the beginning of the reduction reaction (squares) and after 10000 cycles (circles). The graph remarks how weak alloys (left) or strong alloys (right) bind to OH− ions. Pt5Tb, which is the most active electrocatalyst, exhibits compression while approaching the optimum OH binding energy of the Sabatier volcano. Modified with permission from ref 39. Copyright 2016 AAAS.
Figure 2. Colorimetric coordinates when divided into nanometric coordinates by solvation of lanthanide ions using glycerol: (1) [Tb1.0Eu1.0(bdc)3·4H2O]α; (2) [Tb1.8Eu0.2(bdc)3·4H2O]α; (3) 1:1 mixture of [Tb2.0(bdc)3·4H2O]α and [Eu2.0(bdc)3·4H2O]α; (4) [Tb2.0(bdc)3·4H2O]α. Modified with permission from ref 38 Copyright 2015 Wiley-VCH Verlag GmbH & Co. KGaA.
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LANTHANIDES IN BIOLOGY: ALCOHOL METABOLISM PQQ and Ca2+-dependent alcohol dehydrogenases (ADHs) catalyze the two-electron oxidation of alcohols into their corresponding aldehydes. The most accepted mechanism proposed for alcohol oxidation involves a base-catalyzed proton extraction in concert with hydride transfer from the alcohol to the reactive carbon (C5) of the coenzyme PQQ.41 In Ca2+based ADHs, Ca2+ acts as a Lewis acid during catalysis to polarize the bond between the C5 and O5 in PQQ. Tautomerization of the intermediate follows and reduced PQQ is formed. PQQ−ADHs are known to interact with cytochromes, and it has been proposed that PQQ can be reoxidized by transferring two electrons in two steps to a one-electron cytochrome carrier41 (Scheme 1). Metabolism of both methane and methanol requires the oxidation of methanol, which can be catalyzed by MeDHs and methanol oxidases. Until recently, it was thought that numerous methylotrophic bacteria catalyzed methanol oxidation by only
Hybrid Materials. Hybrid materials are the result of coordinating a substrate with a lanthanide metal ion. As the previous examples above highlighted, these compounds can be tunable for their luminescence by changing metal-ion ratios. Examples of these materials include glasses, silicates, nanoparticles, and barcode materials.11 The synthesis of barcode materials is based on cation exchange into fabricated metal− organic framework crystals, while the anionic framework remains intact. The stoichiometry of the metal defines the emission intensity of the material. The successful synthesis of these materials correlates with the intrinsic properties of the lanthanides such as narrow band gaps, sharp and unique emissions, and stability that is independent of the surrounding environments.11 Typical cations exchanged in the crystal matrix are red Eu, green Tb, and orange Sm.11 Finally, to increase the stability of the barcoded material, a coating with silica has proven effective.11 Lanthanide Fuel Cells. Our modern technologies demand sustainable catalysts and energy sources. Lanthanides have been C
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Scheme 1. Currently Accepted Mechanism for Alcohol Oxidation in Quinoproteins Taken from Anthony et al.41
using the well-studied Ca2+-dependent MeDH, MxaFI.42 In 2011, Hibi et al. isolated MeDH from Methylobacterium radiodurans cells grown in a methanol medium containing La3+ and showed that XoxF, and not MxaFI, was responsible for MeDH activity under these conditions.10 From this study, they concluded that XoxF was likely a lanthanide-dependent enzyme. In 2012, Nakagawa et al. showed that XoxF purified from Methylobacterium extorquens AM1 was tightly associated with La3+.43 Subsequently, Pol et al. published the first crystal structure of XoxF purified from Methylacidiphilum f umariolicum SolV, which contained lanthanide ions in the active site (Figure 4).44 Since then, numerous studies have been published
orientation of methanol or PQQ binding in the active site. It is also possible that the acquisition and transport of lanthanides into the cell is limited to specific lanthanides. Further, it has been proposed that the role of lanthanides as Lewis acids and their effect on PQQ is not unique to XoxF.23,24 Good et al. have shown that the activity of the PQQ−ethanol dehydrogenase ExaF is dependent on lanthanides and can oxidize ethanol, formaldehyde, and, to a lesser extent, methanol.24 ExaF only shares ∼53% similarity with XoxF but, like XoxF, uses PQQ as a coenzyme for catalysis. When ExaF contains La3+ in the active site, the ethanol dehydrogenase activity is 900-fold higher than when ExaF is purified from a medium lacking lanthanides.24 Although methanol is not the primary substrate for ExaF, the La3+-dependent methanol oxidation ability of ExaF alone is able to support growth of M. extorquens AM1.24 The ability of lanthanides to facilitate the ExaF activity demonstrates that the biological relevance of lanthanides is not limited to methanol oxidation but has metabolic consequences for multicarbon metabolism as well. We can only predict that these findings are just the beginning of new discoveries surrounding novel lanthanide-dependent enzymes. Lanthanides as Cofactors: Density Functional Theory (DFT) for XoxF. DFT is a theory of electronic structure based on electron density distribution. A recent publication reported DFT studies that demonstrated that when Ce3+- versus Ca2+-containing optimized structures were compared, there was a difference of 0.81 eV in the lowest unoccupied molecular orbital energy of the redox-active PQQ in XoxF from M. f umariolicum SolV.45 Bogart et al. used computational and electrochemical studies to define a correlation between the redox potential reported from numerous complexes in aqueous conditions and the redox potential obtained from computational calculations.45 This correlation allowed the authors to suggest that the potential of the redox pair Ce4+/Ce3+ was extremely sensitive to its crystal field. To extrapolate this correlation to the Ce3+−XoxF interaction, the authors focused on the active site and defined key components of the complexation such as a nine-coordinate Ce cation complexed by a PQQ coenzyme. An unrestricted calculation determined that the most stable redox form was Ce3+-PQQ0 because the spin density was completely localized in a Ce 4f orbital. Finally, DFT studies also estimated that the Ce3+ oxidation potential was potent, with a value of +1.35 V versus saturated calomel electrode. Together, these studies showed that functional model complexes for XoxF reactivity can be guided using redox
Figure 4. Metal and PQQ binding in the active site of ADHs. Detailed view of the amino acids, metal, and PQQ positions in the catalytic sites of (A) MxaF and (B) XoxF. Coordination of the lanthanide is thought to require an additional aspartate residue (in this case, D301) compared to Ca2+ coordination.22
on XoxF enzymes from a variety of organisms,45−49 and XoxF has been suggested to be the predominant MeDH in natural communities.42,50,51 The few published biochemical studies on XoxF enzymes suggest that XoxF-type MeDHs may be able to use both methanol and formaldehyde as substrates.22,46 It has also been proposed that lanthanides enable a higher oxidation capacity of these enzymes over their Ca2+-dependent counterparts. However, the biochemical versatility regarding product formation and the range of lanthanides able to promote catalysis has not been studied in detail. For example, one possibility is that some XoxF-type MeDHs may produce formate by the sequential oxidation of methanol and formaldehyde if a stronger Lewis acid such as La3+ is present, but the final product might be formaldehyde if a weaker Lewis acid such as Sm3+ is present. Phenotypic studies have indicated that only some lanthanides (La3+ to Sm3+) can support methanol growth of methylotrophs.23,52 It is possible that weaker Lewis acids are unable to efficiently polarize C5 of PQQ or that lanthanides heavier than Sm3+ interfere with the proper D
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Inorganic Chemistry energetic calculations from computational analysis when lanthanides and quinone ligands are involved.45 Lanthanide Extraction and Recovery. Employing lanthanides for emerging biotechnologies has become essential for our modern lifestyle because they are components of cell phones, computers, wind turbines, refrigerators, lasers, batteries, GPS equipment, precision guided weapons, MRI equipment, etc. Although consumption of lanthanides is rising, national mining and production has almost ceased in the United States because of high mining costs and the harmful effects of mining on the environment.4,53 Currently, the mining, extraction, and recovery of lanthanides are limited by three factors: (1) mining and extraction are achieved by using harsh conditions such as acid extraction and high temperature, which release toxic and radioactive waste products, (2) lanthanides are found in minerals formed by a lanthanide mixture, and thus chemical separation of each type leads to an inefficient recovery overall, and (3) the extraction efficiency is dependent on ores containing high concentrations of lanthanides, which limits potential sources of recovery.53 There have been extensive efforts to optimize extraction methods and to expand the chemicals that can be used during these processes, but currently the U.S. largely depends on China for its supply of lanthanides.4 The characterization of mechanisms by which microorganisms interact with metals has contributed to the advancement of biotechnological processes for bioleaching (biomining) and bioremediation of other metals such as copper and zinc.54 The recent discovery that methylotrophs can sense, solubilize, and transport lanthanides makes these microorganisms a potential biometallurgic platform for lanthanide recovery. We have recently developed a strain of M. extorquens AM1 that functions as a sensitive fluorescent biosensor of lanthanide presence (La3+ to Nd3+), showing induction of fluorescence with concentrations as low as 2.5 nM exogenous La3+.23 To determine if this strain can “sense” lanthanides from discarded electronics, computer hard-drive magnets were broken into small fragments using a hammer or blender and incubated with the M. extorquens AM1 biosensor strain. Induction of fluorescence was observed after incubation with magnet or Nd3+ but not with other metal ions found in hard-drive magnets or the magnet coating: Fe3+, B3+, and Ni2+ (Figure 5A). As the concentration of the magnet increased, the peak fluorescence intensity decreased. This decrease in fluorescence was likely due to the cytotoxic effects of the other elements like iron that are present at high enough concentrations to turn the medium a rust-like color (Figure 5B). This suggests that M. extorquens AM1 will need to be engineered for metal resistance in order to effectively function as a biorecycling strategy. To determine if M. extorquens AM1 can use lanthanides present in discarded electronics for growth, a mutant strain lacking the Ca2+-dependent MeDH (mxaF null mutant)55 was used so that methanol growth can only occur if lanthanides are obtained. This strain grew in the presence of a magnet or Nd3+ but not with the other metals present in computer hard-drive magnets (Figure 6). These results show that not only can the Nd3+ presence in hard-drive magnets be sensed by methylotrophic bacteria like M. extorquens AM1, but it can be acquired and used for growth. Future efforts will focus on testing whether M. extorquens AM1 can obtain lanthanides from mining ores like Monazite and Bastnäsite and engineering the organism for increased lanthanide recovery and metal resistance. While the use of methylotrophic bacteria may increase lanthanide mining yields and facilitate biorecycling efforts, there
Figure 5. Fluorescent transcriptional reporter fusion23 used as a biosensor of Nd3+ from recycled hard-drive magnets. (A) Expression from the lanthanide-dependent MeDH xox1 promoter using Venusyfp as a transcriptional reporter in M. extorquens AM1. The reporter strain was grown to the middle of the exponential phase in a methanol medium23 and added to sterile tubes lacking or containing one of the following: 2 μM NdCl3, 2 μM FeCl3, or different amounts of crushed computer hard-drive magnet (containing Nd3+, Fe3+, Ni2+, and B3+). Expression levels were measured and reported as relative fluorescent units (RFU) over time, as described previously.23 Representative data from three biological replicates are shown. Fluorescence using 2 μM NiCl2 or 2 μM NaHB4 was also tested and mirrored the no magnet control (data not shown). (B) Metals in the magnet that leached into the growth medium over time, turning the medium a rust color.
Figure 6. Growth of an mxaF mutant strain in a methanol medium lacking or containing one of the following: 2 μM NdCl3, 2 μM FeCl3, or 0.05 or 0.1 g of crushed computer hard-drive magnet. To account for the change in the optical density (OD600) by metals leaching out from crushed magnets, the background OD600 from a growth medium lacking cells but containing 0.05 and 0.1 g of magnet was subtracted from the corresponding bacterial culture OD600. The growth curve shows representative data from three biological replicates. 2 μM NiCl2 and 2 μM NaHB4 were also tested and mirrored the no magnet control (data not shown).
is still the issue of how to separate the recovered lanthanides from one another. Solvent extraction facilitates the processing of high volumes of material but is compromised in purity, while highly pure lanthanides are isolated using ion-exchange extraction methods but only on a small scale. Promising breakthroughs for the efficient and selective separation between heavy and light lanthanides have been recently reported.56 E
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Figure 7. Schematic of displacement phenomena over time during sorption. Reproduced from ref 56. Copyright 2016 American Chemical Society.
Magnetic sorbent nanotechnology has been used to extract metallic cations from aqueous solutions.57,58 The technology principle consists of coating the surface of a magnetic nanoparticle with a chelator. Zhang et al. reported high yields of recovery by using a zerovalent iron nanoparticle coated with two layers, one of silica and a second with silica and poly(allylamine) hydrochloride molecules.56 The chelator, diethylenetriaminepentaacetic acid (DTPA), was covalently attached to the primary amines on the surface of the nanoparticle and used for the sorption.56 This chelator is known to form stable complexes with La3+ under immobilized conditions. An advantage of using magnetic nanosorbents is that all chelating carboxylic acids on DTPA are available for complexation. The authors report a maximal sorption capacity of 120 μmol g−1. Further, a separation factor of 11.5 between heavy and light lanthanides was reported, representing a 10-fold increase in the yield compared to any other separation factor reported to date.56 In addition, the system reached maximum uptake (point where same amounts of heavy and light lanthanides are adsorbed) at 30 min. After 30 min, displacement on the nanosorbent surface of the light lanthanides by the heavy lanthanides was observed (Figure 7). The displacement phenomenon correlates with the DPTA−lanthanide complex stability. Previous studies demonstrated that the DTPA-Ln complex stability increased steadily from La to Sm and then remained constant for the heavy lanthanides.59,60
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Telephone: (517) 884-5406. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS Funding to support the contribution by N.C.M.-G. came from Michigan State University startup funds. E.S. and H.N.V. are supported by a San Jose State University Research, Scholarship and Creative Activity grant and a California State University Program for Education and Research in Biotechnology (CSUPERB) New Investigator Grant.
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REFERENCES
(1) Bünzli, J.-C.G. Lanthanides, Kirk-Othmer Encyclopedia of Chemical Technology; Wiley Online Library: New York, 2013. (2) Cotton, S. Lanthanide and Actinide Chemistry; John Wiley & Sons Ltd.: Chichester, U.K., 2006. (3) Zepf, V.; Simmons, J.; Reller, A. Materials critical to the energy sectorAn introduction; BP plc: London, 2014. (4) Barmettler, F.; Castelberg, C.; Fabbri, C.; Brandl, H. AIMS Microbiology. 2016, 2, 190−204. (5) Harrowfield, J. M. Metal ions in biological systems; Sigel, A., Sigel, H., Ed.; Marcel Dekker: New York, 2003. (6) Silber, H. B.; Paquette, S. J. In Metal ions in biological systems; Sigel, A., Sigel, H., Ed.; Marcel Dekker: New York, 2003. (7) Deliormanlı, A. M. J. Mater. Sci.: Mater. Med. 2015, 26, 67. (8) de Oliveira, C.; Ramos, S. J.; Siqueira, J. O.; Faquin, V.; de Castro, E. M.; Amaral, D. C.; Techio, V. H.; Coelho, L. C.; e Silva, P. H.; Schnug, E.; Guilherme, L. R. Ecotoxicol. Environ. Saf. 2015, 122, 136− 44. (9) Fitriyanto, N. A.; Nakamura, M.; Muto, S.; Kato, K.; Yabe, T.; Iwama, T.; Kawai, K. J.; Pertiwiningrum, A. Journal of Bioscience and Bioengineering. 2011, 111, 146−152. (10) Hibi, Y.; Asai, K.; Arafuka, H.; Hamajima, M.; Iwama, T.; Kawai, K. J. Biosci Bioeng. 2011, 111, 547−549. (11) Shen, X.; Yan, B. J. Colloid Interface Sci. 2016, 468, 220−226. (12) Bünzli, J-C.G. J. Coord. Chem. 2014, 67, 3706−3733. (13) Nief, S. Handbook on the Physics and Chemistry of Rare Earths; Elsevier Science BV: Amsterdam, The Netherlands, 2010. (14) MacDonald, M. R.; Bates, J. E.; Ziller, J. W.; Furche, F.; Evans, W. J. J. Am. Chem. Soc. 2013, 135, 9857−9868. (15) Shannon, R. D. Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 1976, 32, 751. (16) Bratsch, S. G. J. Phys. Chem. Ref. Data 1989, 18, 1.
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CONCLUSIONS Our modern technologies depend on lanthanide chemistry, and as a response, the scientific community is making important contributions toward understanding the mechanistic details of the interaction between lanthanides and ligands, enabling direct applications of these concepts to be developed. The inclusion of lanthanides as cofactors for enzymes involved in the catalysis of central metabolism is very recent. We have demonstrated that lanthanides enhance the activity of ethanol dehydrogenase in addition to the MeDH XoxF and propose to utilize methylotrophic bacteria to facilitate or enhance lanthanide mining and recycling. Together, the applications of biological and chemical strategies for efficient extraction, recovery, and separation of lanthanides are developing areas of study that are likely to improve the yields and purity of lanthanides while informing and implementing environmentally friendly mining and recycling efforts.
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Materials and methods section for the original research presented in this forum and information including chemicals, growth conditions, methodology for the transcriptional reporter fusion methodology, and details of the growth curve analysis (PDF)
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b00919. F
DOI: 10.1021/acs.inorgchem.6b00919 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry (17) Cotton, F. A.; Wilkinson, G. Adv. Inorg. Chem. 1988, 776, 955. (18) Pagano, G.; Guida, M.; Tommasi, F.; Oral, R. Ecotoxicol. Environ. Saf. 2015, 115, 40. (19) Lim, C. S.; Kampf, J. W.; Pecoraro, V. L. Inorg. Chem. 2009, 48, 5224−5233. (20) Rico, C. M.; Barrios, A. C.; Tan, W.; Rubenecia, R.; Lee, S. C.; Varela-Ramirez, A.; Peralta-Videa, J. R.; Gardea-Torresdey, J. L. Environ. Sci. Pollut. Res. 2015, 22, 10551−10558. (21) Goecke, F.; Jerez, C. G.; Zachleder, V.; Figueroa, F. L.; Bišová, K.; Ř ezanka, T.; Vítová, M. Front. Microbiol. 2015, 6, 2. (22) Keltjens, J. T.; Pol, A.; Reimann, J.; Op den Camp, H. J. M. Appl. Microbiol. Biotechnol. 2014, 98, 6163−6183. (23) Vu, H. N.; Subuyuj, G. A.; Vijayakumar, S.; Good, N. M.; Martinez-Gomez, N. C.; Skovran, E. J. Bacteriol. 2016, 198, 1250− 1259. (24) Good, N. M.; Vu, H. N.; Suriano, C.; Subuyuj, G. A.; Skovran, E.; Martinez-Gomez, N. C. J. Bact. 2016. (25) Xu, J. D.; Radkov, E.; Ziegler, M.; Raymond, K. N. Inorg. Chem. 2000, 39, 4156−4164. (26) Zhang, X.; Jiang, J. Rare Earth Coordination Chemistry, Fundamentals and Applications; John Wiley & Sons Ltd., Chichester, U.K., 2010. (27) Bünzli, J.-C.G. Handbook on the Physics and Chemistry of Rare Earths; Elsevier Science BV: Amsterdam, The Netherlands, 1987. (28) Sastri, V. S.; Bünzli, J.-C.G.; Rao, V. R.; Rayudu, G. V. S.; Perumareddi, J. R. Modern Aspects of Rare Earths and Complexes; Elsevier Science BV:Amsterdam, The Netherlands, 2003. (29) Cable, M. L.; Kirby, J. P.; Gray, H. B.; Ponce, A. Acc. Chem. Res. 2013, 46, 2576−2584. (30) Butler, S. J.; Parker, D. Chem. Soc. Rev. 2013, 42, 1652−1666. (31) Zwier, J. M.; Bazin, H.; Lamarque, L.; Mathis, G. Inorg. Chem. 2014, 53, 1854−1866. (32) Charbonnière, L. J. Curr. Inorg. Chem. 2011, 1, 2−16. (33) Parker, D. Coord. Chem. Rev. 2000, 205, 109−130. (34) Gunnlaugsson, T.; Leonard, J. P. Chem. Commun. 2005, 25, 3114−3131. (35) Reid, B. L.; Stagni, S.; Malicka, J. M.; Cocchi, M.; Hanan, G. S.; Ogden, M. I.; Massi, M. Chem. Commun. 2014, 50, 11580−11582. (36) Liu, B.; Huang, Y.; Zhu, X.; Hao, Y.; Ding, Y.; Wei, W.; Wang, Q.; Qu, P.; Xu, M. Anal. Chim. Acta 2016, 912, 139. (37) de Lill, D. T.; de Bettencourt-Dias, A.; Cahill, C. L. Inorg. Chem. 2007, 46, 3960−3965. (38) Neaime, C.; Daiguebonne, C.; Calvez, G.; Freslon, S.; Bernot, K.; Grasset, F.; Cordier, S.; Guillou, O. Chem. - Eur. J. 2015, 21, 17466−17473. (39) Escudero-Escribano, M.; Malacrida, P.; Hansen, M. H.; VejHansen, U. G.; Velázquez-Palenzuela, A.; Tripkovic, V.; Schiøtz, J.; Rossmeisl, J.; Stephens, I. E. L.; Chorkendorff, I. Science 2016, 352, 73−76. (40) Xia, B. Y.; Wu, H. B.; Li, N.; Yan, Y.; Lou, X. W.; Wang, X. Angew. Chem., Int. Ed. 2015, 54, 3797−3801. (41) Kay, C. W. M.; Mennenga, B.; Görisch, H.; Bittl, R. J. Biol. Chem. 2006, 281, 1470−1476. (42) Chistoserdova, L. Environ. Microbiol. 2011, 13, 2603−2622. (43) Nakagawa, T.; Mitsui, R.; Tani, A.; Sasa, K.; Tashiro, S.; Iwama, T.; Hayakawa, T.; Kawai, K. PLoS One 2012, 7, e50480. (44) Pol, A.; Barends, T. R. M.; Dietl, A.; Khadem, A. F.; Eygensteyn, J.; Jetten, M. S. M.; Op den Camp, H. J. M. Environ. Microbiol. 2014, 16, 255−264. (45) Bogart, J. A.; Lewis, A. J.; Schelter, E. J. Chem. - Eur. J. 2015, 21, 1743−1748. (46) Wu, M. L.; Wessels, J. C.; Pol, A.; Op den Camp, H. J.; Jetten, M. S.; van Niftrik, L.; Keltjens, J. T. Appl. Environ. Microbiol. 2015, 81, 1442−1451. (47) Taubert, M.; Grob, C.; Howat, A. M.; Burns, O. J.; Dixon, J. L.; Chen, Y.; Murrell, J. C. Environ. Microbiol. 2015, 17, 3937−3948. (48) Ramachandran, A.; Walsh, D. A. FEMS Microbiol Ecol. 2015, 91, fiv105.
(49) Firsova, Y. E.; Torgonskaya, M. L.; Trotsenko, Y. A. Microbiology 2015, 84, 796. (50) Chistoserdova, M. World J. Microbiol. Biotechnol. 2016, 32, 138. (51) Skovran, E.; Martinez-Gomez, N. C. Science 2015, 348, 862− 863. (52) Chu, F.; Lidstrom, M. E. J. Bacteriol. 2016, 198, 1317−1325. (53) Zhuang, W.-Q.; Fitts, J. P.; Ajo-Franklin, C. M.; Maes, S.; Alvarez-Cohen, L.; Hennebel, T. Curr. Opin. Biotechnol. 2015, 33, 327−335. (54) Ehrlich, H. L. Appl. Microbiol. Biotechnol. 1997, 48, 687−692. (55) Marx, C. J. L.; Chistoserdova, L.; Lidstrom, M. E. J. Bacteriol. 2003, 185, 7160−7168. (56) Zhang, H.; McDowell, R. G.; Martin, L. R.; Qiang, Y. ACS Appl. Mater. Interfaces 2016, 8, 9523−9531. (57) Koehler, F. M.; Rossier, M.; Waelle, M.; Athanassiou, E. K.; Limbach, L. K.; Grass, R. N.; Günther, D.; Stark, W. J. Chem. Commun. 2009, 32, 4862−4864. (58) Kaur, M.; Johnson, A.; Tian, G.; Jiang, W.; Rao, L.; Paszczynski, A.; Qiang, Y. Nano Energy 2013, 2, 124−132. (59) Xie, F.; Zhang, T. A.; Dreisinger, D.; Doyle, F. Miner. Eng. 2014, 56, 10−28. (60) Sui, N.; Huang, K.; Zhang, C.; Wang, N.; Wang, F.; Liu, H. Ind. Eng. Chem. Res. 2013, 52, 5997−6008.
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DOI: 10.1021/acs.inorgchem.6b00919 Inorg. Chem. XXXX, XXX, XXX−XXX
